Glutathione reductase from livers of DBA/2J mice was purified to homogeneity by affinity chromatography. It is a dimeric enzyme of molecular weight 107,000 daltons with a sedimentation coefficient 6.13S, stoke radius 41.8 degrees A and PI equals 6.91. Kinetic studies revealed a ping-pong mechanism. The substrate protects the enzyme against thermal inactivation.